Simon didn't know what it was about you, but everything you did made him just hate you a little bit more. Price loved you, and while he ranked the same as you, and Price liked him as well, Simon couldn't help but resent you for it. He could see the things everyone else turned a blind eye to.
He saw the moments where you'd get a bit too reckless during the missions, almost risking yourself and everyone else on the mission. He simply believed it stemmed from a desire to win, no matter what; and it angered him. Reckless and selfish behaviour had no place in a job like this.
Which meant that when he got sent on a covert operation with you, he was anything but happy about it. Simon wasn't about to save your ass if you did something stupid. Or at least that's what he told himself. Until you actually did do something insanely stupid, and despite what he repeated to himself constantly, he did save you.
"You have to got to be the most dumbest, most reckless person I have ever worked with," he growled, pacing the bunker while lecturing you where you sat huddled in a blanket, soaking wet after you jumped into a river to escape a group of mercenaries. "Are you insane? I specifically said to wait for my signal, and you did the exact bloody opposite of that!"